What’s a dichotomous key? Help

Puccinellia

Lemma measurements should be made on the lower ones of a given spikelet. The orientation of panicle branches should be assessed when the plant is in fruit. Puccinellia nutkaensis (J. Presl) Fern. & Weatherby was reported from ME (under the name P. laurentiana Fern. & Weatherby)  by Angelo and Boufford (1998); however, the specimen was in fact P. pumila— Somes Harbor, Rand s.n. ( MASS!). References: Hughes and Halliday (1980), Davis and Consaul (2007).

Choose this species
P. maritima
1a. Anthers 1.5–2.6 mm long; first glume 2–3.5 mm long; second glume 2.8–4 mm long; spikelets with 5–11 florets; plants often stoloniferous
See list of 4 species in 1b
CHOOSE THIS LEAD
1b. Anthers 0.3–1.5 (–2) mm long; first glume 0.7–2.7 mm long; second glume 1.2–3 mm long; spikelets with 3–9 florets; plants not stoloniferous, or infrequently so in P. pumila (and then usually the result of buried stems)
- Choose this species
  P. fasciculata
  2a. Inflorescence contracted, even the lower branches ascending; spikelets borne in the apical as well as the basal portion of branches; lemma firm at the tip, with an excurrent midrib; anthers 0.6–1 mm long
- See list of 3 species in 2b
  CHOOSE THIS LEAD
  2b. Inflorescence often open, at least the lower branches spreading or divergent; spikelets borne mostly in the apical portion of branches; lemma hyaline and weak at the apex, the midrib evanescent, usually not reaching the tip; anthers 0.7–1.5 mm long
  - Choose this species
    P. pumila
    3a. Branches of the panicle usually smooth or only slightly scabrous; distal margin of the lemma entire or with a few scattered cilia or scabrules [Fig. 265]; caryopsis 1.3–2.1 mm long
  - See list of 2 species in 3b
    CHOOSE THIS LEAD
    3b. Branches of the panicle prominently scabrous; distal margin of the lemma prominently scabrous-ciliate [Fig. 264]; caryopsis 1–1.6 mm long
    - Choose this species
      P. distans
      4a. Lemmas broad-obtuse to truncate at the apex [Fig. 264], the lowest of the spikelet 1.5–2.5 mm long; inflorescence open, the lower branches spreading or reflexed; anthers 0.4–0.8 mm long
    - Choose this species
      P. nuttalliana
      4b. Lemmas acute to narrow-obtuse at the apex, the lowest of the spikelets (2–) 2.2–3 (–3.5) mm long; inflorescence more upright, the branches commonly ascending; anthers 0.6–1.5 (–2) mm long

Show All Couplets

Show photos of: Each photo represents one species in this genus.